This invention relates to an electrostatic shield which is arranged to be incorporated into the applicator head of a conventional diathermy apparatus to effect the significant reduction of the electrostatic field radiated thereby.
Diathermy treatments involve the application of high frequency electric currents to body tissues. This technique utilizes the transcutaneous transmission of high frequency energy to the internal body tissues to be treated. The energy employed is sufficiently high to prevent adverse stimulation of nerves and muscles and is sufficiently low to prevent destruction of the treated tissue.
In a conventional diathermy apparatus, radio frequency electric currents are generated by the apparatus. These high frequency electric currents are then applied to the associated applicator which converts these high frequency currents into electromagnetic and electrostatic energy. The generated electromagnetic and electrostatic energy is then controllably applied by the applicator to the body of the patient. This energy causes heat to be generated within the internal body tissues which are within the radiating range of the applicator.
Painful heating of the subcutaneous fat layer and irritating skin burns may occur when a patient is treated using conventional diathermy apparatus. It has been found that the deleterious surface heating effects just described are primarily caused by electrostatic field radiated by conventional diathermy applicator head. The associated radiated electromagnetic field, however, does not cause the above-mentioned harmful burning of surface tissues. Furthermore, the radiated electromagnetic field penetrates deeply enough to provide relative heating in the muscle tissues without painful burning of the subcutaneous fat layer and skin tissue. This deep heating is at least partially produced because the electromagnetic field lines are tangential to the tissue interfaces rather than perpendicular and, as a result, the boundary conditions do not significantly effect or cause surface heating effects. As a result, the therapeutic deep heating benefits of diathermy treatment are primarily caused by the electromagnetic energy radiated by the applicator head.
By attenuating the electrostatic field radiated by the applicator head before it reaches the patient being treated, it is possible to virtually eliminate the above-described surface heating effects. A technique and apparatus for accomplishing this result are given and described in U.S. Pat. to Berry, et al, No. 4,068,292 entitled "Electrostatic Shield for Diathermy Treatment Head." This patent was issued on Jan. 10, 1978, and is incorporated by reference herein. The shield disclosed in that patent is comprised of a plurality of non-magnetic metallic (preferably copper) strips which are located interiorly of a coplanar, generally circular loop. Each of the strips is maintained at a generally perpendicular orientation with respect to the current carrying coil in the diathermy applicator head on which the shield is mounted. Each of the strips extends generally radially outward from the vicinity of the center of the loop and terminates at and is electrically connected with the circular loop.
It has been found that prior art applicator heads sometimes induce circulating currents in the circular loop of an associated shield. Other shields do not attenuate electrostatic energy which may be radiated outwardly through the sides of the applicator head. As a result, the outer casing of the applicator head prior art designs normally constructed of an electrically conductive material isolate the current carrying coils of the applicator head from external loads but permits circulating currents to be induced in the outer casing of the head.
In many instances the creation of circulating currents with the loop of the shield and the outer casing of the applicator head is highly undesirable and may be responsible for several detrimental effects. In particular circulating currents in the applicator produces an associated power loss which significantly reduces the operating efficiency of the diathermy apparatus. Another problem associated with such circulating currents within the outer casing of the applicator head is that same becomes extremely hot in response to such current flow therein. In fact, the outer casing of the head can become so hot that it is impossible to physically touch the head while the apparatus is in use. Accordingly, the minimization of such circulating currents with the outer casing of the applicator head and the circulating loop of the associated shield is highly desirable.
The present invention provides a unique electrostatic shield which overcomes the aforementioned problems. The electrostatic shield of the present invention includes a plurality of strips of the shield extending around the sides of the radiating coil within the applicator head and terminating the strips in a closed band which is located in a plane well below the coil. In the preferred embodiment of the invention, the shield is comprised of a side portion which encircles the radiating coil in the applicator head and a front portion which is positioned forwardly of the radiating coil. The side portion of the shield is comprised of a closed structure having a hollow interior. The walls of the structure are slotted to provide the plurality of lateral strips with same terminating in a closed band.
The forward or face portion of the shield is comprised of a plurality of nonmagnetic metallic strips which are arranged to extend radially inward from the periphery of the face so as to cover a majority of the surface area defined by the face portion of the shield. Each one of these strips is preferably electrically coupled with one and only one of the lateral strips which make up the side portion of the shield. In this way, each lateral strip and its associated face strips act as a single continuous strip which extend upwardly and which terminate within the area formed by the face portion of the shield.
As a result of this configuration, the electrostatic shield of the present invention provides improved attenuation of the electrostatic field which is radiated by the radiating coil of the applicator head. A primary benefit to be derived from this attenuation of the electrostatic field resides in the significant improvement in the operating efficiency of the diathermy apparatus. In particular, greater attenuation of the electrostatic field by the electrostatic shield of the present invention serves to further reduce electrostatic (capacitive) coupling between the treated body tissues and the applicator head. The reduction or elimination of capacitive coupling between the applicator head and body tissues, stablizes the operation of the diathermy apparatus and thereby reduces the likelihood that the applicator will be detuned from resonance upon an introduction of a load into the radiating region of the applicator head. By stablizing the operation of the diathermy apparatus, it becomes easier to keep the applicator head in electrical resonance thereby improving the accuracy of the power measuremens made by the device.
Use of the subject invention also enhances the operation of the diathermy apparatus by reducing head loss. As mentioned above, the electrostatic shield of the present invention serves to isolate the electrostatic field radiated by the radiating coil in the applicator head from the loop of the shield and from the outer casing of the applicator head. By isolating the electrostatic field in this manner, the creation of circulating currents within the outer loop of the shield and in the outer casing of the applicator head is significantly reduced thereby improving the operating efficiency thereof.
It is therefore an object of the present invention to provide an improved electrostatic shield which is arranged to substantially reduce the intensity of the circulating currents created within the various components of the shield.
Another object of the present invention is to provide an improved electrostatic shield which is arranged to effectively isolate the electrostatic field radiated by the shield's associated applicator head from the outer casing of the applicator head.
A further object of the present invention is to provide an improved electrostatic shield of the character described which is operable to reduce power loss within the applicator head and to thereby improve the operating efficiency of the diathermy apparatus.
A further object of the present invention is to provide an improved electrostatic shield of the character described which is operable to eliminate excess heating of the outer casing of the applicator head.
An additional object of the present invention is to provide an improved electrostatic shield of the character described which is arranged to virtually eliminate electrostatic (capacitive) coupling between the radiating coil within an applicator head and a load within the radiating region of the head.
A further object of the present invention is to provide an improved electrostatic shield of the character described which is arranged to make the reactive parameters of the applicator head less responsive to the surface characteristics of the load within the radiating region of the head thereby stablizing the operation of the diathermy apparatus.
Other and further objects of this invention will become apparent in the course of the following description.